myasthenic

my·as·then·ic

(mī'as-then'ik), Relating to myasthenia.

my·as·then·ic

(mī-as-then'ik) Relating to myasthenia.

myasthenia

(mī″ăs-thē′nē-ă) [ my- + -asthenia] Muscular weakness and abnormal fatigue. myasthenic (-then′ik), adjective

myasthenia gravis

Abbreviation: MG
An autoimmune motor disorder marked by muscular fatigue that develops with repetitive muscle use and improves with rest or with the application of a cold pack. It is caused by antibodies to the acetylcholine receptor in the neuromuscular junction and a decrease in receptor sites for acetylcholine. Because the smallest concentration of acetylcholine receptors in the body is in the cranial nerves, weakness and fatigue of the eye muscles, muscles of mastication, and pharyngeal muscles are the most prominently affected in most patients, but any (skeletal) muscle group may be involved. The disease is rare, affecting about 14 people out of 100,000.

Diagnosis

Diagnosis is made on the basis of patient history, a thorough neurological examination, electromyography, repetitive nerve stimulation, a Tensilon test, or a combination of these tests. Intravenous injection of Tensilon significantly improves muscle weakness within 60 sec, lasting up to 30 min Acetylcholinesterase receptor antibody titers in the blood are elevated in about 50% to 70% of patients with myasthenia gravis.

Symptoms

Clinical signs include ptosis of the eyelid and double vision due to fatigue and weakness in the extraocular muscles, and difficulty chewing and swallowing from impaired facial and pharyngeal muscles. Speech that becomes progressively more dysarthric during prolonged dialogue is another common symptom. Symptoms are exacerbated by repetitive muscle use, and, in some patients, by menses, emotional stress, prolonged exposure to sunlight or cold, and infections. Myasthenia gravis crisis is a sudden exacerbation of symptoms with respiratory failure.

Treatment

The primary treatment is with anticholinesterases and immunosuppressive agents. Anticholinesterase therapy often becomes less effective as the disease worsens. In selected patients, removal of the thymus, plasmapheresis, or immunoglobulin therapy is used.

Patient care

The patient with MG should seek medical attention immediately if he or she experiences difficulty breathing, talking, chewing, or swallowing. These symptoms may herald a myasthenic crisis. In crisis the patient's cardiovascular, neurologic, and respiratory status should be monitored in an intensive care unit. Suctioning the airway and postural changes may sometimes maintain adequate oxygenation and ventilation. If not, the patient will need intubation and positive-pressure ventilation. Exercise, meals, and care activities should be planned around medication-induced energy peaks. The patient should be taught that soft but solid foods are more easily managed than liquids when swallowing is difficult. Additional help for patients is available through support groups and Internet-based resources such as the Myasthenia Gravis Foundation of America (www.myasthenia.org).

CAUTION!

Because edrophonium (Tensilon) occasionally causes significant bradycardia or asystole, atropine should be kept at the bedside of any patient given this medication.

单词	myasthenic
释义	DictionarySeemyastheniaEncyclopediaSeeMyasthenia myasthenic my·as·then·ic (mī'as-then'ik), Relating to myasthenia. my·as·then·ic (mī-as-then'ik) Relating to myasthenia. myasthenia (mī″ăs-thē′nē-ă) [ my- + -asthenia] Muscular weakness and abnormal fatigue. myasthenic (-then′ik), adjective myasthenia gravis Abbreviation: MG An autoimmune motor disorder marked by muscular fatigue that develops with repetitive muscle use and improves with rest or with the application of a cold pack. It is caused by antibodies to the acetylcholine receptor in the neuromuscular junction and a decrease in receptor sites for acetylcholine. Because the smallest concentration of acetylcholine receptors in the body is in the cranial nerves, weakness and fatigue of the eye muscles, muscles of mastication, and pharyngeal muscles are the most prominently affected in most patients, but any (skeletal) muscle group may be involved. The disease is rare, affecting about 14 people out of 100,000. Diagnosis Diagnosis is made on the basis of patient history, a thorough neurological examination, electromyography, repetitive nerve stimulation, a Tensilon test, or a combination of these tests. Intravenous injection of Tensilon significantly improves muscle weakness within 60 sec, lasting up to 30 min Acetylcholinesterase receptor antibody titers in the blood are elevated in about 50% to 70% of patients with myasthenia gravis. Symptoms Clinical signs include ptosis of the eyelid and double vision due to fatigue and weakness in the extraocular muscles, and difficulty chewing and swallowing from impaired facial and pharyngeal muscles. Speech that becomes progressively more dysarthric during prolonged dialogue is another common symptom. Symptoms are exacerbated by repetitive muscle use, and, in some patients, by menses, emotional stress, prolonged exposure to sunlight or cold, and infections. Myasthenia gravis crisis is a sudden exacerbation of symptoms with respiratory failure. Treatment The primary treatment is with anticholinesterases and immunosuppressive agents. Anticholinesterase therapy often becomes less effective as the disease worsens. In selected patients, removal of the thymus, plasmapheresis, or immunoglobulin therapy is used. Patient care The patient with MG should seek medical attention immediately if he or she experiences difficulty breathing, talking, chewing, or swallowing. These symptoms may herald a myasthenic crisis. In crisis the patient's cardiovascular, neurologic, and respiratory status should be monitored in an intensive care unit. Suctioning the airway and postural changes may sometimes maintain adequate oxygenation and ventilation. If not, the patient will need intubation and positive-pressure ventilation. Exercise, meals, and care activities should be planned around medication-induced energy peaks. The patient should be taught that soft but solid foods are more easily managed than liquids when swallowing is difficult. Additional help for patients is available through support groups and Internet-based resources such as the Myasthenia Gravis Foundation of America (www.myasthenia.org). CAUTION! Because edrophonium (Tensilon) occasionally causes significant bradycardia or asystole, atropine should be kept at the bedside of any patient given this medication.
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